![]() ![]() In fig.1 the spectrum, as received on my 145/435 MHz dual band antenna at 45 meter height 10km east of In yellow: signal strengths according to European amateur-norm: S9 = 5uV over 50 ohms, 1Spoint = 6 dB. (20dB less means 10 times weaker, 40dB less means 100 times weaker, 60dB less means 1000 times weaker). The signals at 145-146MHz in figs.1-4 came from different relay-stations, and consequently are different in strength. 1, are 30 times (!!) stronger than our already very strong local Observe that some signals from pager networks in fig. Here some pictures from the radio spectrum below 200 MHz,Īs seen in 2001 on my home build spectrum "analyzer", and received on my 2m/70cm dual band antenna at 45 meters height, 8km west of Rotterdam city center. #146 MHZ BANDPASS FILTER 1 MHZ TV#With optimized suppression of FM- and TV broadcast. Super selective + maximal suppression of 155MHz. Notch, with little increase of insertion loss.Ī simpler wire-coupled helix band pass filter is the best choice to attenuate signals below 145 MHz (FM-broadcast and TV-bandįor 145MHZ. You can build it at very low cost with simple tools.įor still steeper filter flanks and better suppression of signals very close to our two meter band, simply add one 155MHz-cable On the two meters band, a 2 resonator helix band pass filter gives minimal insertion loss, maximal selectivity, and a The coaxial notch filter is easy to make by every radio amateur.įor the construction of the other filters you must perform some simple mechanical work, and be able to measure VSWR and insertion In the articles below you will find construction descriptions for cheap home made filters against such IMD. Noises, caused by inter modulation from their own receiver, due to the intrusion of very strong out of band signals, from data networks (150-165MHz) or FM-broadcast (88-108MHz). Many Many listeners on the two meters band are often hindered by loud ![]()
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